Background Gemcitabine remains a cornerstone in chemotherapy of pancreatic ductal adenocarcinoma (PDAC) despite suboptimal clinical effects that are partly due to the development of chemoresistance. Pancreatic stellate cells (PSCs) of the tumor stroma are known to interact with pancreatic cancer cells (PCCs) and influence the progression of PDAC through a complex network of signaling molecules that involve extracellular matrix (ECM) proteins. To understand tumor-stroma interactions regulating chemosensitivity, the role of PSC-secreted fibronectin (FN) in the development of gemcitabine resistance in PDAC was examined. Methods PSC cultures obtained from ten different human PDAC tumors were co-cultured with PCC lines (AsPC-1, BxPC-3, Capan-2, HPAF-II, MIA PaCa-2, PANC-1 and SW-1990) either directly, or indirectly via incubation with PSC-conditioned medium (PSC-CM). Gemcitabine dose response cytotoxicity was determined using MTT based cell viability assays. Protein expression was assessed by western blotting and immunofluorescence. PSC-CM secretome analysis was performed by proteomics-based LC-MS/MS, and FN content in PSC-CM was determined with ELISA. Radiolabeled gemcitabine was used to determine the capacity of PCCs to uptake the drug. Results In both direct and indirect co-culture, PSCs induced varying degrees of resistance to the cytotoxic effects of gemcitabine among all cancer cell lines examined. A variable degree of increased phosphorylation of ERK1/2 was observed across all PCC lines upon incubation with PSC-CM, while activation of AKT was not detected. Secretome analysis of PSC-CM identified 796 different proteins, including several ECM-related proteins such as FN and collagens. Soluble FN content in PSC-CM was detected in the range 175–350 ng/ml. Neither FN nor PSC-CM showed any effect on PCC uptake capacity of gemcitabine. PCCs grown on FN-coated surface displayed higher resistance to gemcitabine compared to cells grown on non-coated surface. Furthermore, a FN inhibitor, synthetic Arg-Gly-Asp-Ser (RGDS) peptide significantly inhibited PSC-CM-induced chemoresistance in PCCs via downregulation of ERK1/2 phosphorylation. Conclusions The findings of this study suggest that FN secreted by PSCs in the ECM plays a key role in the development of resistance to gemcitabine via activation of ERK1/2. FN-blocking agents added to gemcitabine-based chemotherapy might counteract chemoresistance in PDAC and provide better clinical outcomes. Electronic supplementary material The online version of this article (10.1186/s12885-019-5803-1) contains supplementary material, which is available to authorized users.

BackgroundNeurotensin has been found to promote colon carcinogenesis in rats and mice, and proliferation of human colon carcinoma cell lines, but the mechanisms involved are not clear. We have examined signalling pathways activated by neurotensin in colorectal and pancreatic carcinoma cells.MethodsColon carcinoma cell lines HCT116 and HT29 and pancreatic adenocarcinoma cell line Panc-1 were cultured and stimulated with neurotensin or epidermal growth factor (EGF). DNA synthesis was determined by incorporation of radiolabelled thymidine into DNA. Levels and phosphorylation of proteins in signalling pathways were assessed by Western blotting.ResultsNeurotensin stimulated the phosphorylation of both extracellular signal-regulated kinase (ERK) and Akt in all three cell lines, but apparently did so through different pathways. In Panc-1 cells, neurotensin-induced phosphorylation of ERK, but not Akt, was dependent on protein kinase C (PKC), whereas an inhibitor of the β-isoform of phosphoinositide 3-kinase (PI3K), TGX221, abolished neurotensin-induced Akt phosphorylation in these cells, and there was no evidence of EGF receptor (EGFR) transactivation. In HT29 cells, in contrast, the EGFR tyrosine kinase inhibitor gefitinib blocked neurotensin-stimulated phosphorylation of both ERK and Akt, indicating transactivation of EGFR, independently of PKC. In HCT116 cells, neurotensin induced both a PKC-dependent phosphorylation of ERK and a metalloproteinase-mediated transactivation of EGFR that was associated with a gefitinib-sensitive phosphorylation of the downstream adaptor protein Shc. The activation of Akt was also inhibited by gefitinib, but only partly, suggesting a mechanism in addition to EGFR transactivation. Inhibition of PKC blocked neurotensin-induced DNA synthesis in HCT116 cells.ConclusionsWhile acting predominantly through PKC in Panc-1 cells and via EGFR transactivation in HT29 cells, neurotensin used both these pathways in HCT116 cells. In these cells, neurotensin-induced activation of ERK and stimulation of DNA synthesis was PKC-dependent, whereas activation of the PI3K/Akt pathway was mediated by stimulation of metalloproteinases and subsequent transactivation of the EGFR. Thus, the data show that the signalling mechanisms mediating the effects of neurotensin involve multiple pathways and are cell-dependent.

BackgroundOral squamous cell carcinoma is an aggressive neoplasm with serious morbidity and mortality, which typically spreads through local invasive growth. Lysophosphatidic acid (LPA) is involved in a number of biological processes, and may have a role in cancer cell migration and invasiveness. LPA is present in most tissues and can activate cells through six different LPA receptors (LPAR1-6). Although LPA is predominantly promigratory, some of the receptors may have antimigratory effects in certain cells. The signalling mechanisms of LPA are not fully understood, and in oral carcinoma cells the specific receptors and pathways involved in LPA-stimulated migration are unknown.MethodsThe oral carcinoma cell lines E10, SCC-9, and D2 were investigated. Cell migration was studied in a scratch wound assay, and invasion was demonstrated in organotypic three dimensional co-cultures. Protein and mRNA expression of LPA receptors was studied with Western blotting and qRT-PCR. Activation of signalling proteins was examined with Western blotting and isoelectric focusing, and signalling mechanisms were further explored using pharmacological agents and siRNA directed at specific receptors and pathways.ResultsLPA stimulated cell migration in the two oral carcinoma cell lines E10 and SCC-9, but was slightly inhibitory in D2. The receptor expression profile and the effects of specific pharmacological antagonist and agonists indicated that LPA-stimulated cell migration was mediated through LPAR3 in E10 and SCC-9. Furthermore, in both these cell lines, the stimulation by LPA was dependent on PKC activity. However, while LPA induced transactivation of EGFR and the stimulated migration was blocked by EGFR inhibitors in E10 cells, LPA did not induce EGFR transactivation in SCC-9 cells. In D2 cells, LPA induced EGFR transactivation, but this was associated with slowing of a very high inherent migration rate in these cells.ConclusionThe results demonstrate LPA-stimulated migration in oral carcinoma cells through LPAR3, mediated further by PKC, which acts either in concert with or independently of EGFR transactivation.

Activated pancreatic stellate cells (PSCs) play a central role in the tumor stroma of pancreatic ductal adenocarcinoma (PDAC). Given the limited availability of patient-derived PSCs from PDAC, immortalized PSC cell lines of murine and human origin have been established; however, it is not elucidated whether differences in species, organ disease status, donor age, and immortalization alter the PSC phenotype and behavior compared to that of patient-derived primary PSC cultures. Therefore, a panel of commonly used PSC cultures was examined for important phenotypical and functional features: three primary cultures from human PDAC, one primary from normal human pancreas, and three immortalized (one from human, two from murine pancreas). Growth rate was considerably lower in primary PSCs from human PDAC. Basal collagen synthesis varied between the PSC cultures, and TGF-β stimulation increased collagen synthesis only in non-immortalized cultures. Differences in secretome composition were observed along with a divergence in the DNA synthesis, migration, and response to gemcitabine of PDAC cell lines that were grown in conditioned medium from the various PSC cultures. The findings reveal considerable differences in features and functions that are key to PSCs and in the interactions with PDAC. These observations may be relevant to researchers when selecting the most appropriate PSC culture for their experiments.

Prostaglandins (PGs) such as PGE2 enhance proliferation in many cells, apparently through several distinct mechanisms, including transactivation of the epidermal growth factor (EGF) receptor (EGFR) as well as EGFR-independent pathways. In this study we found that in primary cultures of rat hepatocytes PGE2 did not induce phosphorylation of the EGFR, and the EGFR tyrosine kinase blockers gefitinib and AG1478 did not affect PGE2-stimulated phosphorylation of ERK1/2. In contrast, PGE2 elicited EGFR phosphorylation and EGFR tyrosine kinase inhibitor-sensitive ERK phosphorylation in MH1C1 hepatoma cells. These findings suggest that PGE2 elicits EGFR transactivation in MH1C1 cells but not in hepatocytes. Treatment of the hepatocytes with PGE2 at 3 h after plating amplified the stimulatory effect on DNA synthesis of EGF administered at 24 h and advanced and augmented the cyclin D1 expression in response to EGF in hepatocytes. The pretreatment of the hepatocytes with PGE2 resulted in an increase in the magnitude of EGF-stimulated Akt phosphorylation and ERK1/2 phosphorylation and kinase activity, including an extended duration of the responses, particularly of ERK, to EGF in PGE2-treated cells. Pertussis toxin abolished the ability of PGE2 to enhance the Akt and ERK responses to EGF. The results suggest that in hepatocytes, unlike MH1C1 hepatoma cells, PGE2 does not transactivate the EGFR, but instead acts in synergism with EGF by modulating mitogenic mechanisms downstream of the EGFR. These effects seem to be at least in part G(i) protein-mediated and include upregulation of signaling in the PI3K/Akt and the Ras/ERK pathways.

Pancreatic ductal adenocarcinoma is characterized by a prominent fibroinflammatory stroma with both tumor-promoting and tumor-suppressive functions. The pancreatic stellate cell (PSC) is the major cellular stromal component and the main producer of extracellular matrix proteins, including collagens, which are degraded by metalloproteinases (MMPs). PSCs interact with cancer cells through various factors, including transforming growth factor (TGF)β and interleukin (IL)-1α. The role of TGFβ in the dual nature of tumor stroma, i.e., protumorigenic or tumor suppressive, is not clear. We aimed to investigate the roles of TGFβ and IL-1α in the regulation of MMP profiles in PSCs and the subsequent effects on cancer cell migration. Human PSCs isolated from surgically resected specimens were cultured in the presence of pancreatic cancer cell lines, as well as IL-1α or TGFβ. MMP production and activities in PSCs were quantified by gene array transcripts, mRNA measurements, fluorescence resonance energy transfer–based activity assay, and zymography. PSC-conditioned media and pancreatic cancer cells were included in a collagen matrix cell migration model. We found that production of IL-1α by pancreatic cancer cells induced alterations in MMP and tissue inhibitors of matrix metalloproteinase (TIMP) profiles and activities in PSCs, upregulated expression and activation of MMP1 and MMP3, and enhanced migration of pancreatic cancer cells in the collagen matrix model. TGFβ counteracted the effects of IL-1α on PSCs, reestablished PSC MMP and TIMP profiles and activities, and inhibited migration of cancer cells. This suggests that tumor TGFβ has a role as a suppressor of stromal promotion of tumor progression through alterations in PSC MMP profiles with subsequent inhibition of pancreatic cancer cell migration.

BackgroundIt is important to understand the mechanisms by which the cells integrate signals from different receptors. Several lines of evidence implicate epidermal growth factor (EGF) receptor (EGFR) in the pathophysiology of hepatocarcinomas. Data also suggest a role of prostaglandins in some of these tumours, through their receptors of the G protein-coupled receptor (GPCR) family. In this study we have investigated mechanisms of interaction between signalling from prostaglandin receptors and EGFR in hepatocarcinoma cells.MethodsThe rat hepatocarcinoma cell line MH1C1 and normal rat hepatocytes in primary culture were stimulated with EGF or prostaglandin E2 (PGE2) and in some experiments also PGF2α. DNA synthesis was determined by incorporation of radiolabelled thymidine into DNA, phosphorylation of proteins in signalling pathways was assessed by Western blotting, mRNA expression of prostaglandin receptors was determined using qRT-PCR, accumulation of inositol phosphates was measured by incorporation of radiolabelled inositol, and cAMP was determined by radioimmunoassay.ResultsIn the MH1C1 hepatocarcinoma cells, stimulation with PGE2 or PGF2α caused phosphorylation of the EGFR, Akt, and ERK, which could be blocked by the EGFR tyrosine kinase inhibitor gefitinib. This did not occur in primary hepatocytes. qRT-PCR revealed expression of EP1, EP4, and FP receptor mRNA in MH1C1 cells. PGE2 stimulated accumulation of inositol phosphates but not cAMP in these cells, suggesting signalling via PLCβ. While pretreatment with EP1 and EP4 receptor antagonists did not inhibit the effect of PGE2, pretreatment with an FP receptor antagonist blocked the phosphorylation of EGFR, Akt and ERK. Further studies suggested that the PGE2-induced signal was mediated via Ca2+ release and not PKC activation, and that it proceeded through Src and shedding of membrane-bound EGFR ligand precursors by proteinases of the ADAM family.ConclusionThe results indicate that in MH1C1 cells, unlike normal hepatocytes, PGE2 activates the MEK/ERK and PI3K/Akt pathways by transactivation of the EGFR, thus diversifying the GPCR-mediated signal. The data also suggest that the underlying mechanisms in these cells involve FP receptors, PLCβ, Ca2+, Src, and proteinase-mediated release of membrane-associated EGFR ligand(s).

Grb2-associated binder (Gab) family proteins are docking molecules that can interact with receptor tyrosine kinases (RTKs) and cytokine receptors and bind several downstream signalling proteins. Studies in several cell types have shown that Gab1 may have a role in signalling mediated by the two RTKs epidermal growth factor (EGF) receptor (EGFR) and Met, the receptor for hepatocyte growth factor (HGF), but the involvement of Gab1 in EGFR and Met signalling has not been directly compared in the same cell. We have studied mechanisms of activation and role in mitogenic signalling of Gab1 in response to EGF and HGF in cultured rat hepatocytes. Gab1, but not Gab2, was expressed in the hepatocytes and was phosphorylated upon stimulation with EGF or HGF. Depletion of Gab1, using siRNA, decreased the ERK and Akt activation, cyclin D1 expression, and DNA synthesis in response to both EGF and HGF. Studies of mechanisms of recruitment to the receptors showed that HGF induced co-precipitation of Gab1 and Met while EGF induced binding of Gab1 to Grb2 but not to EGFR. Gab1 activation in response to both EGF and HGF was dependent on PI3K. While EGF activated Gab1 and Shc equally, within the same concentration range, HGF very potently and almost exclusively activated Gab1, having only a minimal effect on Shc. Collectively, our results strongly suggest that although Gab1 interacts differently with EGFR and Met, it is involved in mitogenic signalling mediated by both these growth factor receptors in hepatocytes.